Basis set convergence in second-row compounds: the importance of core polarization functions

Abstract

Using sequences of Dunning's correlation consistent basis sets, cc-pVnZ (n = 3,4,5), convergence of molecular properties is much slower for second-row compounds than for their first-row counterparts, both at the Hartree-Fock and at correlated levels, due to core polarization effects. By adding a single high-exponent d function to the standard cc-pVnZ basis sets, convergence is greatly accelerated. After correcting for core correlation, computed D-0, r(e), and omega(e) values for a number of diatomics generally agree with experiment to better than 0.02 eV, 0.001 Angstrom, and 5 cm(-1), respectively. (C) 1998 Elsevier Science B.V.